[time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)
Bob Camp
kb8tq at n1k.org
Sat Apr 23 12:12:15 UTC 2016
Hi
If you are going to mount an antenna outdoors on a > 100’ cable run … don’t use an automotive mag mount
antenna. Even cheap cable will cost you more than the eBay price of a “real” timing antenna. The antenna it’s
self may not be very fancy. The amp and filter in the antenna likely are much better than the car antenna. The
housing and connector are *way* beyond the mag mount in terns of surviving in the rain / snow / hail / sleet / sunlight/
wind / birds / and so on. There also is the possibility that the timing antenna is better protected against lightning.
On the plus side, it’s easier to get an auto antenna that will run on +3.3V (and blow out at +5). It’s also easier to
find one that will cover Glonass. They are smaller and less obtrusive if the neighbors are a big concern.
Lots of issues !
Bob
> On Apr 22, 2016, at 8:45 PM, Bob Stewart <bob at evoria.net> wrote:
>
> Hi Bob,
>
> There's one thing I forgot to mention: the 5 yards of RG-174 that an active puck antenna usually has connected. That's probably a loss of more than 15DB right off the bat. But, if you're using a puck, you're probably using a short cable to your receiver, so you shouldn't cut the RG-174, otherwise you may overload the receiver's front-end.
>
> Bob
> --------------------------------------------
> On Fri, 4/22/16, Bob Camp <kb8tq at n1k.org> wrote:
>
> Subject: Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)
> To: "Discussion of precise time and frequency measurement" <time-nuts at febo.com>
> Date: Friday, April 22, 2016, 6:17 PM
>
> Hi
>
> Ok, well, let’s over think this a bit
> more:
>
> The antenna has 38 db
> gain. It *might* have a noise figure of 0.7 db. A typical
> modern GPS has < 2db noise figure. Anything over 6 db of
> net
> gain is “good enough”. On that
> basis, a line loss of 32 db would be OK. Your 100 M of quad
> shield at 21 db still gives you enough for three levels of
> passive
> splitter (8 outputs). Yes, it’s
> not going to work with an old Oncore. It will work with the
> new stuff at that level of splitting.
>
> Bob
>
>> On
> Apr 22, 2016, at 6:45 PM, Ryan Stasel <rstasel at uoregon.edu>
> wrote:
>>
>> Bob,
>>
>> Fair enough. I’ll
> just stop worrying about it. =)
>>
>> I believe that number sounds like per 100
> meter, not per 100 foot. Once I have the actual coax, as
> someone suggested, I’ll just hook some ends up, and check
> it. =)
>>
>> Sadly, I
> don’t have an SA, so checking the attenuation might be
> problematic. Though, could I not just use a function gen
> (signal gen), and a scope? Trying to think… I don’t have
> anything that’ll do 1.5Ghz though (or even close).
>>
>> Meh, overthinking…
> what Paul said. =) I’m sure it’ll be fine. Will the
> T-bolt actually complain about poor signal, or just not work
> reliably? And lastly, I guess, there’s a setting on the
> T-bolt to compensate for cable length. I assume that’s
> compensation for antenna cable length? I know I can figure
> that out with an SG and Scope, assuming the propagation
> delay is what the spec sheet claims to be (most RG6 seems to
> be right around 80%) (the home depot stuff seems to be
> 79%).
>>
>> -Ryan
> Stasel
>>
>>> On Apr
> 22, 2016, at 14:38 , Bob Stewart <bob at evoria.net>
> wrote:
>>>
>>> Hi
> Ryan,
>>>
>>> For
> the few years I've been on time-nuts, I understood the
> consensus view to be to get a good quality RG-6QS satellite
> cable. A few of the posts in this thread have made me
> wonder if the consensus is changing, or if it's just too
> much trouble to stand up to the crowd. I've got about
> 300 ft of CerroWire RG-6QS leftover from Home Depot in the
> garage. I looked at the datasheet, and it's
> confusing. For the attenuation at 1000MHz, they list
> 21.45DB per hundred with the superscript "1".
> However there is nothing on the page noting whether that
> "1" means per 100 feet or per 100 meters.
> Looking at the competition it would appear that that's
> per meter. Unfortunately, I don't have the right
> connectors to hook it up to my SA to see. OTOH, 100 ft
> runs from this spool don't show any noticeable (i.e.
> problematic) attenuation of the signal. Maybe someone else
> with a spool of RG-6 in the garage could give use some real
> world attenuation figures at L1?
>>>
>
>>> But, rather than over-engineering
> or over-angsting this issue, it's probably OK to just
> pick one and use it. It's not likely to make any real
> difference unless you have a run in the many hundreds of
> feet.
>>>
>>> Bob
> - AE6RV
>>>
>>>
> --------------------------------------------
>>> On Fri, 4/22/16, Ryan Stasel <rstasel at uoregon.edu>
> wrote:
>>>
>>>
> Subject: Re: [time-nuts] RG6 or LMR400 for GPS Antenna
> (Symmetricom 58532A and T-bolt)
>>> To: "Discussion of precise time
> and frequency measurement" <time-nuts at febo.com>
>>> Date: Friday, April 22, 2016, 4:09
> PM
>>>
>>> Paul,
>
>>>
>>> LOL! So,
> along those lines…
>>> one other
> question, since I can’t find my belden, I’ll
>>> be buying some coax. Anyone have any
> opinions about RG6 for
>>> CCTV vs
> CATV? My understanding is the CCTV version always
>>> has a solid copper center conductor
> (which in my mind would
>>> mean less
> voltage loss for the DC power going to the
>>> antenna), or I’m still overthinking
> it and should just go
>>> with standard
> RG6?
>>>
>>>
> Thanks!
>>>
>>>
>
>>> -Ryan Stasel
>>>
>>>> On Apr
> 21, 2016, at 13:04
>>> , paul swed
> <paulswedb at gmail.com>
>>> wrote:
>>>>
>
>>>> Ryan a
>>> slight heads up.
>>>> Time Nuts is not about
>>> time accuracy as many people
> assume.
>>>>
>>> Its actually about the time we all
> waste looking for what we
>>> know we
> have.
>>>> We just measure that
> time
>>> accurately.
>>>> I do not use anti seize.
>>> Nothing against it just one more glob
> of stuff to
>>>> deal with.
>>>> If you use
>>> the heat shrink and it seals your done
> for my 2 cents.
>>>> Paul
>>>> WB8TSL
>>>>
>>>> On
> Thu, Apr 21, 2016
>>> at 1:07 PM, Ryan
> Stasel <rstasel at uoregon.edu>
>>> wrote:
>>>>
>
>>>>>
>>>
> All,
>>>>>
>>>>>
>>>
> Really awesome answers, thanks!
>>>>>
>>>>> For the sealing question, it
> was more
>>> of a “should I bother
> with something
>>>>> like
> anti-seize” or the like on the
>>>
> actual thread-thread N interface. The
>>>>> actual connector crimp, was
> planning
>>> on just using a couple
> layers of the
>>>>> heat-shrink
> with adhesive. That is all
>>> going to
> be internal to the mast
>>>>>
>>> anyway, so direct weather contact
> should be minimal. It’s
>>> also on
> the side
>>>>> of my chimney,
>>> that gets very little to no direct
> sun, so UV exposure
>>>>> should
> be minimal. But good note on
>>> that
> regard.
>>>>>
>>>>> Pete, thank you very much for
> the info
>>> wrt the antenna and amp,
> and also
>>>>>
>>> the fact the Trimble starter kit came
> with RG6. I’m going
>>> to see what
> my
>>>>> seller wants for
>>> LMR400, but otherwise, I’ll just use
> RG6. It’s
>>> certainly
>>>>> easier to handle. I did
>>> find some datasheets on the stuff that
> Home despot
>>>>> (har har) sells
> (Southwire (
>>>>> http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheetOEM80)).
>>>>> I swear I have a box of
> Belden
>>> somewhere, but I can’t
> seem to find it.
>>>>>
>>>>> Thanks
>>> again!
>>>>>
>>>>>
>>>
> -Ryan Stasel
>>>>>
>>>>>> On Apr 21, 2016, at 06:02
> , paul
>>> swed <paulswedb at gmail.com>
>>> wrote:
>>>>>>
>>>>>> With respect to sealing.
> Everyone
>>> has a method.
>>>>>> I use what I
>>> learned in the Navy. I could see how
> well the connections
>>>>>
> held
>>>>>> up
>>> in the worst conditions sun cold heat
> wet humidity...
>>>>>> Layer
> of rubber tape
>>>>>> scotch
> kote
>>>>>> Layer of plastic
> tape
>>>>>> scotch kote
>>>>>> If done well the
> connector
>>> releases just fine even
> after 5 or more
>>>>> years. I
>>>>>>
>>>
> want to say 10. But then woodpeckers have a way of
>>> shortening the life of
>>>>>>
>>>
> connectors and coax.
>>>>>>
> The
>>> approach is really layers and
> the top to deteriorate over
>>>
> time...
>>>>>> But as I say
> everyone
>>> has their own approach.
>>>>>>
>>>
> Regards
>>>>>> Paul
>>>>>> WB8TSL
>>>>>>
>>>>>> On
>>> Wed, Apr 20, 2016 at 9:03 PM, Ryan
> Stasel <rstasel at uoregon.edu>
>>>>> wrote:
>>>>>>
>>>
>
>>>>>>> Bob/Paul,
>>>>>>>
>>>>>>> Thanks. And
> there's the
>>> rub... Who knows
> what the specs are on
>>>
> "generic"
>>>>>>>
> RG6 QS.
>>> I'll see what my seller
> wants for their LMR400, but
>>>
> otherwise
>>>>> yeah,
>>>>>>> RG6 is just easier. I
> have
>>> both compression and crimp
> connectors for it,
>>>>>>>
> including some RG6
>>> N-connectors
> (yeah, they're probably for LMR300, but
>>>>>>> they work).
>>>>>>>
>>>>>>> Other question: any
> tips for
>>> the exterior N connection?
> I can
>>>>>>>
> "weatherproof" the
>>> actual
> cable-connector crimp, but I'm curious if
>>>>> anyone
>>>>>>> bothers to
> "lube"
>>> the N connector to
> keep moisture from otherwise
>>>>> seizing
>>>>>>> it up.
>>>>>>>
>>>>>>> Thanks!
>>>>>>>
>>>>>>> Ryan Stasel
>>>>>>> IT Operations Manager,
> SOJC
>>>>>>> University of
> Oregon
>>>>>>>
>>>>>>> Sent from my iPhone
>>>>>>>
>>>>>>>> On Apr 20, 2016,
> at 17:00,
>>> Bob Camp <kb8tq at n1k.org>
>>> wrote:
>>>>>>>>
>>>>>>>> Hi
>>>>>>>>
>>>>>>>> RG-6 Quad Shield
> should be
>>> fine as long as it’s
> meeting the published
>>>>>>> specs. The advantage
> of
>>> LRM-400 is that you likely
> *know* where it came
>>>>>>> from and what the
> specs
>>> are.
>>>>>>>>
>>>>>>>> If you decide to
> split the
>>> antenna between
> GPSDO’s, a powered splitter
>>>>>>> is a really good idea.
> Each
>>> time you split another 2 ways,
> you loose 3
>>>>> db.
>>>>>>>
>>> Get at least a 4 way splitter ….
>>>>>>>>
>>>>>>>> Bob
>>>>>>>>
>>>>>>>>> On Apr 20,
> 2016, at
>>> 4:41 PM, Ryan Stasel
> <rstasel at uoregon.edu>
>>> wrote:
>>>>>>>>>
>>>>>>>>> All,
>>>>>>>>>
>>>>>>>>> I’m going to
> be
>>> installing a “permanent”
> antenna at home, and will
>>>>>
> need
>>>>>>>
>>> a run of about 100ft to get from my
> workstation, to the mast
>>> I’ll
> be
>>>>>>> mounting the
>>> antenna on (Symmetricom 58532A).
> I’ve seen some
>>> indication
>>>>>>> that both the
>>> antenna and the Trimble Thunderbolt
> won’t have any
>>> issues
>>>>>>> with running over
>>> 75ohm cable, but thought I’d ask the
> “experts”
>>> whether
>>>>>>> I’d be better off
>>> with some RG6 Quad-shield, or LMR400
> (I’ve got a local
>>>>>>>
> source that doesn’t know
>>> what
> LMR400 is, or what it’s worth)?
>>>>>>>>>
>>>>>>>>> Obviously
> I’d prefer
>>> to run and crimp RG6,
> but if I’d be better off
>>>>>>> with LMR400, I’d
> rather run
>>> that now than go back
> into the crawlspace
>>>>>>>
> again. =)
>>>>>>>>>
>
>>>>>>>>> Also, if
> it helps,
>>> I’ll probably have a
> Symmetricom/HP 58516A at/near
>>>>>>> the T-bolt so I can
> experiment
>>> with other GPS(DO)s as
> well (especially
>>>>> one
>>>>>>>
>>> of the JRMiller boards I bought and
> built (but never
>>> finished) ages
>>>>> ago).
>>>>>>> Which brings the
> question,
>>> will the T-bolt provide
> the oomph needed to
>>>>>>>
> power that splitter and the
>>> antenna
> over that length of cable?
>>>>>>>>>
>>>>>>>>> Thanks!
>>>>>>>>>
>>>>>>>>> -Ryan
> Stasel
>>>>>>>>>
>>>>>>>>>
>>>>>>>>>
>>>
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>>>
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